Method for Producing a Tension Member, Tension Member, and Use Thereof

ABSTRACT

The invention relates to a method for filling in a tension member in particular for conveyor belts, in particular a tension member which is configured as a steel cable. The method is intended to allow the full penetration of the tension member structure. Here, the method contains at least the following method steps:—introducing the individual wires ( 2, 2′, 2″, 2′″, 2″″ ) of the strand ( 5 ) into the stranding head ( 1 ) of a stranding machine ( 10 ) and—partially or fully applying at least one coating agent to at least 50% of the individual wires ( 2, 2′, 2″, 2′″, 2″″ ) of the strand ( 5 ) prior to the twisting of the individual wires ( 2, 2′, 2″, 2′″, 2″″ ) to form a strand ( 5 ) or simultaneously with the twisting of the individual wires ( 2, 2′, 2″, 2′″, 2″″ ) to form a strand ( 5 ) and—twisting the individual wires ( 2, 2′, 2″, 2′″, 2″″ ) to form a strand ( 5 ), wherein at least 50% of the individual wires ( 2, 2′, 2″, 2′″, 2″″ ) have been provided with at least one coating agent, and—making a cable from at least one strand ( 5 ).

The invention relates to a method for producing a tension member, inparticular for conveyor belts, in particular a tension member which isconfigured as a steel cable.

Conveyor belts have a bearing-side and a running-side cover plate, eachfrom a polymer material having elastic properties, and an embeddedtension member in the form of cables that in the longitudinal directionof the conveyor belt run in parallel and that may be constructedsubstantially from steel.

The tensile-force transmitting carcass of a conveyor belt is composed oftextile and/or steel cable inserts which are typically surrounded by atleast one adhesive rubber mixture. The carcasses are surrounded on allsides by wear-resistant rubber cover plates and a rubber edge protector.Additionally, various penetration-protection installations may also bepresent if required.

Conveyor belts where the carcass consists essentially of steel cablesare known as steel-cable conveyor belts. Steel-cable conveyor belts canmake excellent transport performance possible even under very adverseconditions. Their robust construction guarantees both high breakingstrength when very high levels of conveying performance are required andalso good resistance to harsh treatment. They are generally particularlyabrasion-resistant, rot-resistant, and corrosion-resistant, andresistant to chemicals and to heat, thus ensuring a long lifetime withlittle need for maintenance.

The arrangement of the steel cables in the steel-cable conveyor beltmostly takes the form of a layer in a plane between the cover plates.For reasons related to adhesion and to prevention of corrosion, thesteel cables are often galvanized cables, mostly with a diameter from2.8 to 16.0 mm, and can be composed of about 40 up to 250 individualwires.

In order to improve adhesion, adhesive mixtures, also known as adhesiverubber mixtures, are often also used, intended not only to optimizeadhesion as such but also to flow into the steel cables during thevulcanization process in order to allow better sealing. Full penetrationthrough the entire cable, also known as full rubberization, is essentialfor the lifetime of the steel cable and therefore also for the entireconveyor belt. If full rubberization does not take place, cavities inthe cable construction remain open, and it is thus possible that, by wayof example, liquids such as water, oils, etc. can migrate within thecable, and progressive oxidation processes, in particular corrosion, canoccur, with increased aging and premature failure of the entire conveyorbelt. Full penetration of the entire cable construction becomes moredifficult as the diameter of the cable increases.

In “closed” cable constructions, which are also known as parallel-lay orlang-lay constructions it is almost impossible to achieve fullpenetration even with relatively small diameters.

Various approaches are known for coating in particular steel cables. Onthe one hand, a sheathing may be applied to the cables, for example, seeinter alia DE 44 38 420 A1, DE 690 29 389 T2, or DE 79 36 995 U1.

However, this leads to the disadvantages that have already beenmentioned above. The production of an open steel cable construction inwhich the production is performed by a complex method in a targetedmanner while forming additional microgaps into which the rubberizationmass may enter during later rubberization is described in DE 694 21 090T2, for example.

The object of the invention therefore lies in providing a method forproducing a tension member that guarantees complete rubberization of thecable such that the number of open cavities is significantly reduced,and thus transportation or migration, respectively, of liquids into thecable construction and above all within the cable construction may beprevented.

The object is achieved in that the method comprises at least thefollowing method steps:

-   -   introducing the individual wires of the strand into the        stranding head of a stranding machine; and    -   applying at least one coating agent partially or completely in        each case to at least 50% of the individual wires prior to        twisting the individual wires to form a strand, or        simultaneously with twisting the individual wires to form a        strand; and    -   twisting the individual wires to form a strand, wherein at least        50% of the individual wires are provided with at least one        coating agent; and    -   making a cable from at least one strand.

Coating of the entire tension member is typically performed in animmersion bath. To date, the entire tension member, or the producedcable, respectively, has usually been simply immersed in the immersionbath and pulled out again therefrom. On account thereof, however, only asheathing on the tension member has been configured, as has already beenmentioned at the outset. In comparison with the coating of the alreadycompleted cable and/or tension member, as has already been mentionedabove, it has surprisingly been found that complete rubberization of thecable and thus also of the tension member arises when the individualwires from which the strand is constructed are already provided with acoating during production of the individual strands of the cable.

This may be performed in a surprisingly simple and cost-effective mannerprior to the wires being twisted in a stranding machine.

Complete penetration has until now been difficult in particular in thecase of closed cable constructions, and not at all possible in the caseof specific cable constructions.

The tension member for the conveyor belt is constructed from at leastone cable which is typically composed of a plurality of strands which inturn are composed of individual wires. The cables may be present as astranded cable or as a helical cable according to DIN EN12385-2:2002+A1:2008. They may be lang-lay cables or cross-lay cables.

The strand may preferably be configured as a round strand, asingle-layer strand, a Seale, a Warrington, a

Filler, a combined parallel-lay, or a compressed strand according to DINEN 12385-2:2002+A1:2008.

The most popular constructions of the cable are 7×7, having one cable of7 strands which each are composed of 7 wires, 1×19+7×7, having a corestrand of 19 individual wires and outer strands each of 7 wires, and7×19, having one cable of 7 strands, wherein each strand is composed of19 wires.

The production of the strands for the tension member is performed bymeans of a stranding machine, also referred to as a stranding device.Both single as well as double-lay stranding machines may be employed.

According to the invention, in a first method step the individual wiresof the strand to be produced are initially introduced into the strandinghead of the stranding machine. From there, said individual wires areguided to the twisting unit of the stranding machine. In a firstvariant, prior to the actual twisting of the individual wires to form astrand in a further subsequent method step, at least one coating agentis in each case applied partially or completely to at least 50%, that isto say to at least half the number, of the individual wires. In a secondvariant, in a simultaneous method step that, however, is to beconsidered as being separate, at least one coating agent is in each casepartially or completely applied to at least 50% of the individual wiresduring the actual twisting of the individual wires to form a strand. Thecoating agent is preferably applied completely in each case to at least50%, that is to say to at least half, of the total amount of individualwires. Particularly preferably 80%, very particularly preferably all, ofthe individual wires, that is to say 100% of the individual wires eachare partially or completely coated. In the ideal case, thus 100% of theindividual wires, that is to say all individual wires, are providedcompletely with a coating agent.

The application of the coating agent may be performed using all knownpossibilities. Said application may be performed by spreading, brushing,injecting by means of an injector or an injection device, respectively,or else by spraying, for example by way of a spray device.

This may be performed manually or mechanically by way of a respectivedevice. In this way, injecting may be performed through a simple lateralbore in the twisting unit, for example.

At an industrial scale, injecting and/or spraying have/has been provento be simplest and most cost effective.

The amount of coating agent is to be chosen such that completerubberization is guaranteed either immediately or else at the latestafter the last process step, for example vulcanization of the finishedproduct (for example of the transportation belt), such that the numberof cavities is significantly reduced.

To this end injecting or else spraying is particularly suitable, sincethey both cause a particularly good uniform application of the coatingagent, during which the thickness of the coating on the individual wiresmay also be readily set.

The wires which are provided in such a manner with a coating agent aretwisted to form a strand, and are made into a cable in a further processstep.

In particular, the core strand of the cable is preferably produced fromthe wires that have been provided with the coating agent.

The number of the individual wires for the strand, and the number of thestrands for the cable herein depend on the desired construction of thetension member.

Depending on the construction, there is the possibility for the finishedcable to be coated yet once more from the outside, or else for theentire cable to be provided with the coating mass during the cablingprocess, so as to reduce any cavities between the strands that may stillexist.

The cable is preferably a steel cable, or a steel-hybrid cable, in whichat least 20% by volume of the cable is composed of steel.

Thus, the individual wires of the strand are preferably composed ofsteel or of a steel-hybrid material, for example of an alloy or similar.Or else, the strand may be composed of individual wires composed ofsteel, and of individual wires composed of a second material that is notsteel.

The tension member coated as per the method according to the inventionis preferably used for producing conveyor belts or transportation belts,but may also be used in every application where filled steel cables areadvantageous. A difference is often made in the literature betweenconveyor belts and transportation belts. Conveyor belts are typicallyemployed for bulk material (such as coal, ores, sand, cement, etc., forexample), while transportation belts are usually utilized for piecegoods (parcels etc.).

In general, conveyor belts are longer, wider, thicker, and stronger thantransportation belts. However, the two terms are often confused in thegeneral usage of language. The present invention is thus suitable bothfor conveyor belts as well as for transportation belts in which in eachcase cables that are constructed substantially from steel are employed.

The coating agent used, or the coating mass used, respectively, isselected depending on the material of the tension member and theconstruction thereof. To this extent, all known coating materials may beused.

The coating agent is preferably based on at least one elastomer. Theelastomer may be rubbers or else thermoplastic elastomers such aspolyurethane, for example. However, it is preferably a rubber selectedfrom the group consisting of natural rubber (NR) and/or butadiene rubber(BR) and/or chloroprene rubber (CR) and/or styrene-butadiene rubber(SBR) and/or nitrile rubber (NBR, HNBR) and/or butyl rubber (IIR) and/orethylene-propylene rubber (EPM) and/or ethylene-propylene-diene rubber(EPDM) and/or polyacrylate rubber (ACM) and/or epichlorohydrin rubber(ECO) and/or chlorosulfonated polyethylene rubber (CSM) and/or siliconerubber (MVQ) and/or fluoro rubber (FPM). The mentioned types of rubbermay here be employed singularly or as blends. Mixtures based on SBRand/or NR and/or BR are particularly well suited as coating agents. Inone preferred embodiment, the coating agent also contains at least onesoftening agent and/or at least one solvent, by way of which theviscosity and/or the adhesion or the stickiness, respectively, of thecoating mass may typically be set. However, it is also possible for thecoating agent to be free from softening agents and/or solvents.

A further advantage of the method according to the invention lies inthat coating agents having relatively high viscosities may also beemployed. This leads to a reduction in softening agents and/or solvents.Complete rubberization of the cable is guaranteed by coating theindividual wires prior to twisting to form a strand.

Coating agents which after vulcanization of the conveyor belt have apore structure are particularly well suited.

This pore structure may be effected by employing chemical propellantsand/or microspheres which are mixed into the coating. Both inorganic andorganic compounds may be employed as a propellant. The propellantsherein are usually pore-forming propellant gases such as azo and diazocompounds, for example, which under the influence of heat or catalystssplit off gases (N₂ or CO₂, for example), and thus enable the formationof pores. The propellants herein disintegrate at a specific temperatureduring processing, with gas formation, or upon the addition of volatilesolvents during polymerization or vulcanization, respectively. Themicrospheres are hollow balls from glass, phenolic resin, carbon, or athermoplastic plastics material, having a diameter in the pm range. Themicrospheres are commercially available in the already expanded form, orelse in the expandable form. In order for an increase in volume of thecoating to be able to be achieved that leads to optimization of therubberization, expandable microspheres which are filled with apropellant and expand when heated are preferably used. Microspheres ofthis type are marketed under the name Expancel® by the Akzo Nobelcompany, for example.

A combination of expanded and expandable microspheres is possible.

The invention is to be explained in more detail by means of a FIGURE,without being limited thereto.

FIG. 1 shows the method according to the invention by means of aschematic illustration. The individual wires 2, 2′, 2″, 2′″, 2″″ areintroduced into the stranding head 1 of the stranding machine 10. Priorto, or during twisting of the individual wires 2, 2′, 2″, 2′″, 2″″ inthe twisting unit 4, at least one coating agent is applied by means ofan injector or an injection device 3. A strand 5 results after theindividual wires 2, 2′, 2″, 2′″, 2″″ have been twisted in the twistingunit 4.

LIST OF REFERENCE SIGNS (PART OF THE SPECIFICATION)

10 Stranding machine

1 Stranding head

2, 2′, 2″, 2′″, 2″″ Individual wires

3 Injector, or spray device

4 Twisting unit

5 Strand

1.-9. (canceled)
 10. A method for producing a tension member, the methodcomprising: introducing individual wires into a stranding head of astranding machine; applying at least one coating agent at leastpartially to at least 50% of the individual wires; twisting theindividual wires to form a strand; and making a cable comprising thestrand; wherein the at least one coating agent is applied prior totwisting the individual wires to form the strand, or simultaneously withtwisting the individual wires to form the strand; wherein the coatingagent comprises expanded microspheres; and, wherein the tension membercomprises the cable.
 11. The method as claimed in claim 10,characterized in that the coating agent is applied partially orcompletely to at least 80% of the individual wires of the strand. 12.The method as claimed in claim 10, wherein the at least one coatingagent is applied completely to at least 50% of the individual wires. 13.The method as claimed in claim 10, wherein the application of thecoating agent is performed by way of an injector, a spray device, orcombination thereof.
 14. The method as claimed in claim 10, wherein thecoating agent further comprises expandable microspheres.
 15. The methodas claimed in claim 10, wherein the strand forms a core strand of thecable.
 16. The method as claimed in claim 10, wherein the cable is asteel cable or a steel-hybrid cable.
 17. The method as claimed in claim10, wherein the cable is a steel-hybrid cable.
 18. A method forproducing a tension member, the method comprising: introducingindividual wires into a stranding head of a stranding machine; applyingat least one coating agent at least partially to at least 50% of theindividual wires; twisting the individual wires to form a strand; andmaking a cable comprising the strand; wherein the at least one coatingagent is applied prior to twisting the individual wires to form thestrand, or simultaneously with twisting the individual wires to form thestrand; wherein the coating agent comprises expanded microspheres; and,wherein the tension member comprises the cable.
 19. The method asclaimed in claim 18, characterized in that the coating agent is appliedpartially or completely to at least 80% of the individual wires of thestrand.
 20. The method as claimed in claim 18, wherein the at least onecoating agent is applied completely to at least 50% of the individualwires.
 21. The method as claimed in claim 18, wherein the application ofthe coating agent is performed by way of an injector, a spray device, orcombination thereof.
 22. The method as claimed in claim 18, wherein thecoating agent further comprises expanded microspheres.
 23. The method asclaimed in claim 18, wherein the strand forms a core strand of thecable.
 24. The method as claimed in claim 18, wherein the cable is asteel cable.
 25. The method as claimed in claim 18, wherein the cable isa steel-hybrid cable.
 26. A tension member comprising at least onecable, the at least one cable comprising at least one strand, wherein50% of individual wires forming the strand are provided with at leastone coating agent, and wherein the coating agent comprises microspheres.27. The tension member as claimed in claim 26, wherein the microspheresare expanded.
 28. The tension member as claimed in claim 26, wherein themicrospheres are expandable.
 29. The use of a tension member as claimedin claim 26, for producing a conveyor belt.